Recovery and separation of naphthalenes by solvent extraction



March 17, 1959 D. B.-BROUGHTON 2,

RECOVERY AND SEPARATION OF NAPHTHALENES BY SOLVENT EXTRACTION Filed Nov.15, 1956 Bottoms 9 Watqr Make -up Ref/ax- Make-up Solvent I N VE N T 0R:Donald B. Bmughtan Fead Stock.

A r p/my: rs.-

United States Patent RECOVERY AND SEPARATION OF NAPH THALENES BY SOLVENTEXTRACTION Application November 15, 1956,,Serial No. 622,488

14' Claims. (Cl. 260-674) This invention relates to a process forseparating and recovering bicyclic aromatic hydrocarbons from mixturesof the same with, other classes of hydrocarbons, such as hydrocarbonmixtures containing said naphthalenes and one or more of the groupcomprising parafiins, naphthenes, olefins: and aromatics. Morespecifically, this invention concerns a process for recovering anextract comprising naphthalene and one or more of its homologs from amixture'of hydrocarbons containing the same and thereafter segregatingthe extract into specific homologs by means. of a process which involvesliquid-liquid phase extraction ofthe hydrocarbon mixture with a solventfor the, naphthalene component selected from the alcohols, the alkyleneglycols, and the polyalkyl'ene glycols, recovering the hydrocarbonsolute from the resulting rich solvent stream and thereafterfractionally distilling the recovered extract to separate saidnaphthalene and homologs.

The principal object of this invention, therefore, is to provide aprocess for segregating substantially pure naphthalene products, each ofwhich consists essentially of an individual" naphthalene homolog frommixtures of the same with other types of hydrocarbons, including othernaphthalene homologs. Other objects of the invention concern thepreparation of individual naphthalene homologs from petroleum sources ina substantially pure form containing at least 99+% of the individualnaphthalenes.

In one of its embodiments this invention comprises contacting ahydrocarbon fraction boiling from about 300 to about 500 F., containingat least two homologous naphthalene hydrocarbons with asolvent for saidnaphthalene hydrocarbons selected from the group consisting of alcohols,an alkylene glycol, a polyalkylene glycol and ethers of said alcohol andglycols at a temperature sufilcient to extract from said hydrocarbonfraction substantially all of said napthalene hydrocarbons therefrom,providing sutficient pressure to maintain the hydrocarbon mixture andsolvent in substantially liquid phase, thereby forming a rich solventcontaining the naphthalene components of said hydrocarbon fractiondissolved in said solvent, counter-currently contacting said richsolvent with a reflux comprising a liquid paraffinic hydrocarbon havinga boiling point below the boiling point of the naphthalene hydrocarbon,separating said rich solvent from a rafiinate comprising nonaromatichydrocarbons, stripping a hydrocarbon extract from the rich solvent,separately recovering lean solvent and said hydrocarbon extract,recycling said lean solvent to said first-mentioned contacting step, andseparating a naphthalene homolog from said hydrocarbon extract.

A more specific embodiment of this invention concerns a'process forseparating naphthalene and methylnaphthalene from ahydrocarbon fractionboiling within the range-of from about 400 'to about 500 P. whichcomprises subjecting said petroleum fraction to countercurrent contact"with an aqueous solution of diethylene glycolcontaining not more thanabout-5% by weight of 2,878,261 Patented Mar. 17, 1959 water at atemperature of from about 325 to aboutAOO? F. and at a pressuresufiicient to maintain said fraction and said solution substantially inliquid phase and form thereby a rich solvent stream containing saidnaphthalene and methylnaphthalene dissolved therein, countercurrentlycontacting said rich solvent stream with a reflux stream comprising anormally liquid parafiinic hydro: carbon having a boiling point lessthan naphthalene, thereafter recovering a rich solvent stream from.which the non-aromatic and alkylbenzene components boiling in thefeedstock rangehave been displaced by contact of said richysolvent withsaid parafiinic hydrocarbon, reducing the pressure on said rich solventstream atsllbstantially isothermal conditions, withdrawing from a, richsolvent, residue a first, vapor fraction comprising; said parafiinichydrocarbon and recycling, saidgfirst fraction to contact with said richsolvent as at least a. portion of said parafi'lnic reflux hydrocarbon,fractionally distilling a naphthalene hydrocarbon from said residue,withdraw ing a bottoms comprising lean solvent, recycling said leansolvent to the first-mentioned contacting zone; as said diethyleneglycol solvent and thereafter fractionally dis tilling thenaphthalene-hydrocarbon fractionto thereby segregate naphthalene fromits homologs.

Other embodiments of the present invention relating to specific aspectsof the present process will be-referred to in greater detail in thefollowing further descriptionof the invention.

It has previously been known that aromatic hydro? carbons, includingpolycyclic aromatics, may be. ex; tracted from certain boiling rangehydrocarbon fractions containing the Same in admixture withparafliniqolefinic and/or naphthenic hydrocarbons by dissolving, thearomatic hydrocarbon in a solvent, such; as an alcohol or glycol, but ithas also been realized that the recoveryof the aromatic hydrocarbon fromthe rich solvent stream formed by contacting the hydrocarbon, fractionwith the solvent does not readily release. its aromatic solute by simpledistillation methods, except at relatively, high temperatures, at whichtemperatures the character of the solvent changes rapidly, tending tobecome highly acidic (presumably because of the adsorptionof oxygenand/or the shift of oxygen atoms in, the molecular coin}: position ofthe alcohol or glycol solvent from hydroxyl and/or ether oxygen tocarboxylgroups) and also,ten d-, ing to becomescontaminated withresinous and tarry. by; products, The acidic contaminants are highlycorro-l sive atthe high temperatures utilized in the extraction and/ orstripping stages and the resins and tars precipitate in the equipment,necessitating frequent interruptionsin the process for the removal ofthe resulting deposits. In effect, therefore, the use of the highlyeffective alco: hols, alkylene glycols and polyalkylene glycols assolvents for the extraction of, polycyclic, aromatics which are re,-}coverable from the rich solvent stream formed in. the extractor only atrelatively high temperatures is madeuna available because of thetendency of the solvent toundere go deterioration into saidacidic,resinous, and tarry. by. products at the required hightemperatures; the use of, such solvents is therefore impracticablebecause of the,

constant and recurring problem of cleaning the eqnip creases, therequired temperature of operation likeyvise increases and thedeterioration of the solvent into acidic;

by-products likewise increases. In accordance with one of the provisionsof the process of this invention a, blanket of inert gas is maintainedover the surface ofthe, glycol which would normally contact atmospheric,oxy gen, thereby excluding oxygen from, contact with glycol andeliminating the deterioration of the solvent to acidic by-products whichcause corrosion of the portions of the equipment coming'into contactwith the solvent and the deposition ofresinous and tarry materials inthe solvent .reboilers and redistillation equipment. The use of-theinert gas blanket in the present high temperatures for .such solventextractions is the inthalene and its homologs are of relatively highmelting point and would normally tend to crystallize in theextractreceiver as they distill out of the rich solvent. Thesenaphthalenes are also of greater density than water and therefore form alower, solid phase in the extract receiver below the aqueous layerdistilled with thenaph In accordance with the process of this inventiona liquid parafiin diluent, in suf-' ficient quantity to completelydissolve the naphthalenes in thalenes from the rich'solvent.

the receiver vessel, is maintained at all times in the receiver vesselto prevent crystallization of the naphthalenes and to reduce theirdensity below that of water .so that the aqueous distillate is presentinthe receiver at troduction of a ,light,.- parafiinic hydrocarbon having-a boiling point below, that of the naphthalene extract into theextractor at a critical point and maintaining the-light 'parafiin in theextract receiver vessel as a diluent of the naphthalene extract, .At therequired extraction temperatures, that is, at temperatures of 200 F. andhigher, the rich solvent stream formed within the extraction zone andcontaining dissolved naphthalenes increase the solubility of otherhydrocarbons (including the normally rafiinate-type hydrocarbons, whichin the absence of the naphthalene solute would be substantiallyinsoluble in alcoholic and glycolic solvents) to such an extent that theentire feed stock becomes soluble in the lower portion of theextraction-3 column, thereby rendering the entire process inoperable assmeans of separating the desired naphthalene and its homologs from othertypes of aliphatic and aromatic hydrocarbons which accompany thesenaphthalenes. in the feed stock. By means of the present process, a.countercurrently flowing reflux stream comprising a light paraflinichydrocarbon is charged into the lower portion of the extraction columnto provide a separate and distinct raffinate phase capable of extractingthe non-aromatic constituents of the feed stock and the non-naphthalenearomatics from the rich solvent stream in the lower portion of theextraction zone and thereby maintain a separate liquid hydrocarbon phaseinto which the rafiinate hydrocarbons dissolved in the rich solvent may,diffuse and which may be removed as a separate liquid phase from the topof the extraction column. In the absence of the light paraflin reflux inthe bottom portion of the extraction zone, the maintenance of a separaterafiinate phasein the extraction zone and the recovery of the presentnaphthalene products becomes inoperable. The boiling pointcharacteristic of the light paraffin reflux enables these hydrocarbonstobe readily distilled from the naphthalene extract recovered in thestripping zone and also enables it to be distilled as a light overheadfrom the rich solvent in the stripping zone without appreciablyvaporizing the naphthalene solute therewith. The preferred lightparaflins comprising at least a portion of the reflux charged into theextractor are the parafiins boiling from about 10 to about 150 F. belowthe boiling point of naphthalene, one of the preferred paraffins forthis use being one or a mixture of C to C parafiins, such as a fractionof petroleum. In the process as herein provided, the light vaporoverhead from the rich solvent stream distilled in the stripping zone,hereinafter described, is rich in the light paraffins present in therich solvent by virtue of having displaced heavier feed stock rafiinatecomponents from the rich solvent in the preceding extraction stage. Thisoverhead, which also contains some of the naphthalene and other aromaticcomponents of the rich solvent stream constitutes a major source of thelight paraffin reflux stream recycled to the extraction zone.

Another feature of the present process, inherent in the use of a lowmolecular weight paraffinic reflux which makes feasible the operation ofthe process is the presence of the light parafiin in the naphthaleneproduct receiver vessel attached to the stripping column. Naphall timesas a lower layer, thereby facilitating withdrawal of both thenaphthalenes and the aqueous phase from thereceiver vessel. The lightparaffin is subsequently readily distilled from the naphthalene extractin the re ceiver forv recovery and recycle of the paraffin reflux in theprocess and for producing a residue consisting of substantially purenaphthalene product.

Another feature of the present process which makes the operation of anaphthalene extraction process feasible is the use of a solvent selectedfrom a specific class of organic compounds containing a certain limitedproportion of, water which adjusts the selectivity and solubilityrelationships of the solvent to the naphthalene compo :nents as well asto the non-aromatic components of the feed stock in such manner as tomake possible. an $60? nom-ically feasiblerange of solvent to feed stockratios,

N and enables the recovery of a naphtha'lene and methyl? naphthaleneproduct in the form of an extract of substantially purity, while at thesame time maintaining the boiling point of the solvent at a. temperaturewhich may be feasibly utilized in a solvent extraction.

and extract recovery process of this'type, including the stripping stageas well as the extraction stage of the process. The water content of thesolvent lies within a certain specified range which reduces the boilingpoint of thesolvent below the decomposition point of the solvent and yetmaintains its selectivity and solvency at a high level. h

Suitable feed stocks utilizable in the process of this invention. arehydrocarbon mixtures generally containingany recoverable proportion ofnaphthalene, methylnaphthalene, or higher naphthalene homologs (hereinreferred to collectively as naphthalene hydrocarbons) in admixture withother hydrocarbons of aromatic, parafiinic or olefinic structure and ofany molecular weight. These mixtures are desirably recovered frompetroleum sources or the conversion products of petroleum, the fractionsutilized as feed stock boiling at least above about 300 F. and morepreferably, from about 400 to about 500 F. The. latter boiling rangeincludes more specifically the desired products of the present process,including naphthalene, having a boiling point of about 424 F.,alphamethylnaphthalene having a boiling point of about 473 F., andbeta-methylnaphthalene which boils at approximately 466 F., althoughhigher boiling feed stocks con taining the higher alkylated homologs ofnaphthalene, such as dimethylnaphthalene isomers, ethylnaphthalene anddiethylnaphthalene may be utilized in the present process as the sourceof the desired product. The feed stock may contain one or morenaphthalenes and/or homologs, but in the preferred application of theprocess, the feed stock is prefractionated to separate a fractioncontaining not more than two species within the range of boiling pointsfor these species. Thus, a fraction boiling from about 400 to about 500F. contains naphthalene and the alphaand beta-methylnaphthalene isomersand an extract product separated from such a feed stock may befractionally distilled in the final stages of the process to segregateindividual isomers and homologs of substantially 100% purity. Feedstocks which are particularly adapted to the present processare selectedfrom the naturally occurring hydrocarbon mixtures ornaphthalene-containing mixtures which are the product or a.-;.fractionof the product of a hydrocarbon conversion process; and which boil. ataconstant temperature as an azeotrope normally inseparable by simple orfractional distillation means. Thus, the conversion products of bydrogen reforming and many other. petroleum refining processes containparaflinic, olefinic, aromatic and naphthenic hydrocarbons having a widerange of molecular weights, depending upon the boiling range of such afraction, which, when distilled yield azeotropic mixtures containingcomponents of the same molecular weight of adjacent homologs.Illustrative of such a separation problem is the segregation ofnaphthalene and the alphaand beta-methylnaphthalene homologs from afraction boiling from 400 to about 500 F., saidfraction containing, inaddition to said naphthalene homologs, aromatic hydrocarbons containinga total of, from 5, tov 7 carbon atoms in alkyl side, chains attached.to the benzenoid nucleus, as well as dodecane, various dodecane isomers,tridecane, and triand tetradecane isomers, as well as variousalkylcyclohexanes, alkylcyclopentanes, etc. Particularly preferredsources of feed stock herein are petroleum or petroleum conversionproduct fractions in which the non-aromatic components are exclusivelyof parafiinic and/or naphthenic structure.

The solvents utilized in the present process which are selectivelymiscible with naphthalene hydrocarbons and therefore capable ofselectively extracting said naphthalenes from mixtures containing thesame, together withparaflinic, olefinic and naphthenic hydrocarbons arereferred to herein as the monoand dihydric alcohols and ethers. Thesecompounds are herein specifically selected for use as solvents becauseof the stability of these compounds at the high temperatures requiredfor ('JXlIl'ElC-r tion of the present hydrocarbon feed stocks which boilat temperatures above about 300 F. Typical representative alcoholsutilizable as solvents for the extraction of naphthalene hydrocarbonsfrom hydrocarbon mixtures are the aliphatic alkanols containing from 1to about carbon atoms, such as methanol, ethanol, n-propanol,isopropanol, n-butanol, sec.-butyl alcohol, tert.-butyl alcohol, amylalcohol, isoamyl alcohol, n-hexanol, cyclohexanol, n-heptanol,n-octanol, lauryl alcohol and the various isomers thereof. The compoundsherein referred to as glycols and utilizable as solvents in the presentprocess include the polyhydric alcohols, such as ethylene glycol,propylene glycol, trimethylene glycol, butylene glycol, amylene glycol,glycerol, beta-methylglycerol, etc. and particularly the dihydric glycolethers, commonly referred to as the polyalkylene glycols, including, forexample, diethylene glycol, (HOCH CH OCH CH OH), triethylene glycol,[HO(CH CH O) H], tetraethylene glycol, [HO(CH CH O) H], dipropyleneglycol, tripropylene glycol, and mixed ethylene glycol-propylene glycolethers. Another class of compounds utilizable herein as solvents are thealcohol ethers of the foregoing monoand polyhydric alcohols andpolyalkylene glycols, particularly the methanol, ethanol, butanol, etc.ethers of monoand diethylene glycol, known commercially as the carbitolsand cellosolve derivatives of these glycols. These materials areselectively miscible with aromatic hydrocarbons, on a comparative basis,that is, to the straight-chain and naphthenic hydrocarbons. Thedifference in the selectivity of the solvent for aromatic hydrocarbonsand aliphatic saturated or naphthenic hyd'rocarbons may be enhanced byincorporating in the solvent composition certain limited amounts ofwater, for example, up to about 20%, and preferably up to about 10%, byweight of the solvent composition of water when enhancing theselectivity between bicyclic aromatics and non-aromatic hydrocarbons, asin the present process. The solvency may also be varied by compoundingthe foregoing alcohols, ethers and glycols into a solvent composition,for example, by mixing diethylene. glycol with diprcpylene glycol in.order to enhanee the solvency of the'..composition for thehydrocarbonmixture; without seriouslyfderogating; its selectivityfornaphthalene hydrocarbons, the quantity of hydrocarbons dissolved by thesolvent composition increasing as the proportion of glycol containingthe longer alkylene groups increases. Particularly preferredsolventcompO: sitions, for operation of the presentprocess are thosewhich contain from about 1% to about 30% by weight of dipropyleneglycol, from 2% to about.5%v by weight of. water and the balancediethylene glycol orv triethylene glycol. Also preferred for use in theextraction of naph thalene and methylnaphthalene from hydrocarbonfractions containing the same isthe solvent composition con.- sisting ofdiethylene or triethylene glycol. containing from 0.5% to about 10% by.weightof' water.

The relationship between solubility, volatility and selectivity ofvarious, aromatiehydrocarbons present in a typical feedstock utilizablein the. presentprocess, for example, a fraction boiling from about400 F.to about 500 F. of a hydroreformed gas oil fraction, based on a solventcomposition containing 98.2% diethylene glycol and 1.8% water, isillustrated by the data in the follow ing table, these data being basedon an extraction tempera: ture of 375 F. and on the basis, of thehydroreformed charge stock containing. about 20% naphthalene and about26% alphaand beta-methylnaphthalenes by weight, as a typical feed stock,and at the above values as typical of the operating temperature andcomposition of solvent. It is to be emphasized, however, that such dataare merely exemplary of typical conditions, the volatility and solvencyrelationships for the indicated aromatics being within the same rangefor other glycol solvents and the relative diiferences in theseproperties being of the same order of magnitude, regardless-of theidentity of the glycol or of the extraction conditions.

TABLE I Extraction of 400-500" F. boiling range petroleum naphtha withdiethylene glycol containing 1.8% water at 375 F.

Rel. Soly.

at Extraction Conditions B. P. Hydrocarbon Component F.,'

to be Extracted Normal Rel. Volat. in Absence of Solvent Rel. Volat. inPresence of Solvent Naphthalene a-methyl-naphthalenefl-methyl-naphthalene Monooylclic Aromatics:

fi-Oarbon atoms alkyl in alkyls 7-Oarb0n atoms in alkyls These dataindicate the feasibility of a solvent extrac? tion process forseparating naphthalene and methylnaphe thalene from a mixture ofhydrocarbons containingthem as well as the C11, C and C mono andpolyalkyl monocyclic aromatic hydrocarbons and aliphatic parafiins. Itwill be noted from the above data that of all of the aromatics presentin the petroleum naphtha, the naphthalenes are most soluble in theglycol solvent, being, on an average, more than twice as soluble as thealkylbenzenes having boiling pointsinvthe same boiling range as thenaphthalenes. This solubility relationship permits substantiallycomplete recovery of the indicated naphthalenes in substantially pureform, free of monocyclic aromatic impurities, particularly in view ofthe boiling points of the aromatics when dissolved in the rich solvent(i. e., the relatively lesser volatility of the naphthalenehydrocarbons. in the presence of the solvent than the monocyclicaromatics). The efiect of the latter factor is to enable completevaporization of the monocyclic aromatics present in the rich solventstream formed in the extraction. column from the rich solvent: by takingoverhead from the rich solvent stripper a first vapor fractionrelatively richer in said monocyclic aromatics '(these being the lowestboiling aromatics in the presence of the solvent of all the aromaticsdissolved in the rich solvent), continuing the rich solvent strippinguntil the rich solvent is free of monocyclics, and thereafter (but onlyafter freeing the rich solvent of dissolved monocyclics) vaporizing intoa separate stripper side-cut fraction the remaining naphthalenes in ahigh state of purity. Any naphthalenes removed from the rich solventinto the vapor overhead fraction of the stripper are recovered therefromwhen the vapor overhead is recycled as a reflux stream to the lowerportion of the extraction zone. The naphthalenes thus refluxed into theextraction zone and contacted with the rich solvent stream just prior toits removal from" the extraction into the stripping zone also serve todisplace non-aromatic and monocyclic alkyl aromatic raflinate-type feedstock hydrocarbons from the rich solvent by virtue of the selectivesolubility of said naphthalenes in the solvent, these rafiinate-typecomponents thereby being displaced into the raflinate stream removedfrom the top of the extraction zone.

The above operating procedures and a fuller description of theprinciples of operation involved in the present process are furtherillustrated and described by reference to the accompanying flow diagram.

The process of the accompanying diagram is directed to a combinedsolvent extraction, rich solvent stripping and extract fractionationprocess utilizing an aqueous alkylene or polyalkylene glycol solvent ina countercurrent solvent extraction process wherein a reflux streamcomprising a relatively volatile paraffin is utilized for the purpose ofdisplacing feed stock raifinate components from the rich solvent streamformed in the extraction vessel. The feed stock, hereinbeforecharacterized, is charged into the process flow through line 1 inamounts controlled by valve 2, being transferred by means of pump 3 intoheat exchanger 4 wherein the hydrocarbon stream is heated to the desiredextraction temperature, generally to a temperature of from about 200 toabout 450 F., preferably to a temperature of from about 300 to about 400F., and thereafter charged at a pressure sufficient to maintain the feedstock in substantially liquid phase, generally, not substantially inexcess of about 300 pounds per square inch, preferably at a pressure offrom about 10 to about 150 pounds per square inch, through line 5 into acountercurrent, liquid-liquid solvent extraction zone designated asextractor 6 in the accompanying diagram, the feed being introduced at apoint in the extraction vessel between the raffinate outlet in the upperend of the column and the rich solvent outlet in the lower portion ofthe column, preferably into the midportion or middle tray of the column.Extraction vessel 6 may be of any suitable type for obtainingcountercurrent contact between the relatively more dense lean solventphase introduced into the upper portion of the column and the relativelyless dense liquid hydrocarbon phase introduced into the column below thesolvent inlet. The hydrocarbon phase accordingly rises in countercurrentflow relationship through the more dense solvent phase which flowsdownwardly through the column. The solvent which is an alkylene glycolcontaining from about 0.5% to about 20% by weight of water, is chargedat a temperature of from about 200 to about 500 F., preferably at atemperature of from about 320 to about 400 F. into extractor 6 from line7 which conveys a recycle lean solvent stream from the extract stripper,hereinafter described, at approximately the stripper reboilertemperature into the extraction zone. In order to maintain the refluxstream, solvent and feed stock in substantially liquid phase in theextraction zone and to provide the advantages of flash distillation inthe stripper and isothermal operation of the process the pressuremaintained in the extraction zone is substantially in ex cess of thepressure maintained in the stripping zone, here- 7 inafter described,and as previously indicated is preferably within the range of from about10 to about pounds per square inch, depending upon the extractiontemperature. The solvent initially introduced into the process flow andany additional quantities required to replace solvent losses are chargedinto line 7 through line 8 in amounts controlled by valve 9. As theliquid phase solvent descends through the rising stream of hydrocarbonsintroduced through line 5, it selectively extracts from the hydrocarbonstream substantially all of the aromatic components present in the feedstock. Thus, as the hydrocarbon phase flows upwardly through the c0lumnit becomes progressively leaner in bicyclic aromatic components,although richer in less preferentially dissolved alkylbenzenes, theultimate hydrocarbon residue removed from the top of the extraction zonethrough line 10, herein referred to as raflinate, consisting almostexclusively of non-aromatic and alkylbenzene hydrocarbons present in theinitial feed stock and introduced by way of the reflux stream. Theraflinate is separately treated, as hereinafter more fully described.

Although the glycol solvent selectively extracts the naphthalenecomponents of the feed stock, including its homologues, the solventnevertheless dissolves to a certain limited extent the alkylbenzenes andnon-aromatic paraffin, olefin and/or naphthene constituents also presentin the'feed stock, the non-aromatic content of the solute present in therich solvent stream being sufficient in amount to contaminate the finalproduct with an impurity (from the standpoint of being a contaminant ofthe desired naphthalenes) boiling at approximately the same temperatureas the desired aromatics. For the purpose of removing the latter, smallamount of impurity from the rich solvent stream prior to the strippingstage, a countercurrently flowing reflux stream comprising relativelyvolatile paraifins (i. e., boiling at a temperature below the initialboiling point of the feed stock) is contacted with the rich solventstream for the purpose of displacing the feed stock non-aromaticimpurities from the rich solvent with parafi'ins which may besubsequently easily separated from the rich solvent and/ or the aromaticextract as a separate and distinct fraction. As heretofore indicated,the reflux stream comprises one or more paraflinic hydrocarbons (such asa light fraction of a paraflinic gasoline) boiling below the initialboiling point of the feed stock (preferably at a temperature from about50 to about 150 F. below the feed stock initial boiling point). In theprocess utilizing, for example, a feed stock boiling from about 400 toabout 500 F., a suitable reflux paraffin may consist of a mixture ofoctanes or the octane-decane fraction of a saturated gasoline or anaphthene boiling from 10 to about 150 F. below the initial boilingpoint of the feed stock such as methylcyclohexane, dimethylcyclohexane,etc. This reflux stream which is made up largely of the light vaporoverhead from the rich solvent stripping column, as hereinafterdescribed, is introduced into extraction Zone 6 in the lower portionthereof, preferably contacting the rich solvent just prior to theremoval of the latter from the bottom of the column, the refluxhydrocarbon thereafter flowing upwardly in countercurrent relationshipto the descending rich solvent in extraction zone 6, the portion inexcess of that which replaces the feed stock raflinate solute of therich solvent joining the raffinate components of the feed stock whichleave the extraction column through line 10. In such countercurrentcontact between the reflux and rich solvent streams, the raifinate-typealkylbenzenes and non-aromatics boiling at approximately the sametemperature as the desired aromatic product are displaced from the richsolvent and their place taken by the reflux hydrocarbon which maysubsequently be readily separated from the aromatic extract product bysimple fractionation. In the illustration of the process shown in theaccompanying drawing the reflux hydrocarbon is charged into extractor 6through line 1 1 in amounts controlled by valve 12, the

As a consequence of recycling the stripper overhead,

this. stream contains, in addition to the light paraflins, a substantialproportion of the most volatile. aromatics extracted from the feedstock. These aromatics are. re dissolved in the solvent by virtue of therecycle ofv overhead to the lower portion of extraction vessel 6 as areflux stream and its contact with the solvent stream in said zone 6.That portion of the paraffin components of the reflux, however, whichdoes not enter the rich solvent stream, (i. e., the amount in excess ofthat required to displace feed stock rafflnate solute of the richsolvent), appears in the raflinate removed. from the top of theextraction vessel through line 10. These excess light paraflins aredesirably, recovered from the.

ratfinate stream for recycle into the process and for this purpose, andin accordance with the present process, they are separated and recoveredfor recycling from the eflluent raflinate stream by any suitable methodof separation. Since the paraflins. utilized herein as. reflux have aboiling point substantially below the boiling point of the feed stock, aconvenient method of separation comprises fractionally distilling thesame from the raflinate stream, although other methods of separation bymeans known to the art may also be employed. For the purpose offractionally distilling the raflinate, the latter stream is conveyed bymeans of pump 16 through line in amounts controlled by valve 17 intoline 18, through heater 19 and line 26) into raflinate, still 21, whichis generally in the form of a suitably packed or bubble tray column. Therafl'inate which is heated to a temperature above the boiling point ofthe reflux component in heater 19 flashes upon entering column 21, theflashed vapors being taken overhead through line 22, liquefied incondenser 23 to a. condensate stream removed from condenser 23 throughline 24, valve-v 25, and drained into receiver 26. A portion of theliquid condensate comprising the desired light paraflin refluxhydrocarbon is recycled to the upper section of fractionating column 21,that portion being withdrawn from receiver 26 through line 27,. divertedinto line 28. in amounts controlled by valve 29 by means of. pump 30 anddischarged through line 31 onto an upper plate of column 21 for use assaid distillation reflux. The remaining portion of the condensate inreceiver 26, com prising said light parafiin overhead of column 21 isdischarged in controlled amounts, determined by valve 32,

into light paraffin reflux recycle line 11. The high boiling bottoms orresidue of the raflinate from which the recycle reflux has been removedas overhead is. reboiled by removal from the bottom of distillationcolumn 21 through line 33, circulated through reboiler heater 34, andthe resulting vaporized portion of the bottoms returned to column 21through line 35. The, raflinate residue comprising the alkylbenzene andparaffinic, nonextracted portion of the feed stock is removedifromreboiler 34 through line 36 and valve 37 for discharge from the processflow. The non-extracted residue of the feed stock may be withdrawn fromthe process flowfor further conversion into aromatic, components byadditional reforming or permanently withdrawn from the process, asdesired.

The rich solvent. stream. formed in extraction vessel 6 and from whichthe feed" stock rafl'inate components have, been displaced. bycountercurrent contact withthe light paraflin-containing reflux in thelower portion of extraction vessel 6 is withdrawn from column 6 throughline 38 in amounts controlled by valve 39 and transferred 7 by means ofpump 40 into line41 which conveys the rich solvent into the upper,flashing section of extract stripper column 42. Stripping zone 42 is inthe form ofv a distillation column having a flash section in the upperportion and a fractional distillation section in the lower portion, thetwo sections being divided by a side-to-side pan sealed into the upperportion of the column from the distillation section below it, asillustrated by interior pan 43 in column 42. The pressure maintained inthe flashing section above pan 43 is somewhat less than the pressure onthe rich solvent stream flowing into stripping vessel 42, such that uponentering column 42 onto pan: 43, the most volatile solute components inthe rich solvent, that is, the light paraflin components, immediatelyflash from the rich solvent by virtue of the sensible; heat content ofthe rich solvent, thereby providing sub stantially isothermal strippingof the solute from the rich. solvent. Also present in the light vapors,because of their'significant (although substantially lower) vaporpressures at the temperature of the rich solvent are water vapor,substantially all of the monocyclic aromatic components in the extract,a smaller proportion of the naphthalene components extracted by thesolvent and a still smaller proportion of the solvent component which,

has the lowest vapor pressure. This relationship in the volatilities ofthe solute components is shown in the data of Table I, particularly thedata relating to the relative volatilities of the various aromatichydrocarbon feed stock components in the presence of the solvent,

the data indicating that the alkylbenzenes are, on an. average, the mostreadily vaporized components ofv the; rich solvent, naphthalene, whichis the most volatile.

bicyclic aromatic in the presence of the solvent. also constitutes asubstantial proportion of the vapor overhead;

from stripper 42, the methylnaphthalene isomers con-.

stituting the least prevalent component. It is evident,

therefore, that all of the monocyclic aromatics will. vaporize from therich solvent prior to any substantial, vaporization of the naphthalenesor, at least, constitute,

a major aromatic hydrocarbon component of the; over.- head vapor. Theseare removed from column 42 through light vapor overhead line 44, passingthrough valve 45 into condenser 46. wherein they are condensed into a.

liquid condensate which are transferred by line 47 into receiver vessel48 wherein the phase of greatest density, comprising aqueous solvent,settles from an upper hydrocarbon layer in vessel 48. The non-vaporizedportion. of the rich solvent stream accumulating on side-to-side. pan 43is removed from the primary flashing section of column 42 at a reducedpressure. (relative to the extrac tion pressure) through line 49 andvalve 50 and discharged at a somewhat lower pressure than the pressure.maintained in the primary flashing section of column 42 onto a lowertray of column 42, the vapors released isothermally from the richsolvent stream at said lower" pressure being removed from the lattersecondary flash.

zone through line 51 and valve 52 and discharged into overhead vaporline 44. The secondary flash vapors thus recovered from column 42comprise the remaining reflux paraflins contained in the rich solvent,additional steam primary flashsectionis preferably a major drop inpres.- I sure (say, one half to two-thirds of the. pressure ditferentialbetween the extraction pressure and the distillation pressure in. column42), the remaining one half to one 1 I third in the pressure drop takingplace in the secondary and subsequent flash sections, if desired.

The secondary flash vapors join the primary flash vapors in line 44,being liquefied in condenser 46 with the primary overhead flash vaporsand thereafter accumulate in receiver vessel 48 with the primary vaporoverhead. The combined hydrocarbons of the primary and secondary flashzones which separate as an upper layer in receiver vessel 48, and whichalso consist of light parafiin reflux, as well as the aromatichydrocarbons vaporized in part from the rich solvent steam aretransferred as reflux stream by means of pump 53 from receiver vessel 48through line 54 and valve 55 into line 13 for recycle into the lowerportion of extraction vessel 6 through line 11, as previously described,the light parafiins and aromatics stripped from the rich solvent invessel 42 being returned to extractor 6 for recovery of the naphthalenehydrocarbons contained in the light vapor overhead and for displacementof feed stock raffinate components in the rich solvent stream, aspreviously described. Since the aromatics in this stream are redissolvedin the rich solvent by recycle as a portion of the reflux stream intoextraction zone 6, a gradual build-up of monocyclic aromatics in therecycle into excessively large quantities of total recycle would resultunless a portion of this stream were continuously removed from theprocess flow and not recycled. For this purpose a bleed line 13acontaining valve 132), is provided as a draw-off line from recycle line13 to'remove that portion of the extract representing the alkylbenzenecomponents of the reflux recycle redissolving in the rich solvent.

The lower aqueous phase accumulating in receiver vessel 48 Whichcontains a small proportion of the monoor polyhydric alcohol sloventcomponent vaporized from the rich solvent stream in the flashingsections of strip ping vessel 42, accumulates in settling leg 56 ofreceiver 48 as a heavy liquid layer and is continuously drainedtherefrom through line 57 in amounts controlled by valve 58, into line59 for reconstituting the aqueous component of the solvent compositionprior to recycling the lean solvent to extraction vessel 6 and toprovide stripping steam in the reboiling section of column 42. Anyadditional water required for replacement of water loss andreconstitution of the lean solvent composition to its desired watercontent may be introduced into the process fiow from storage from line60 in amounts controlled by valve 61. The water thus added to thesolvent is desirably introduced into the reboiling section of column 42in the lower portion of the column, the water thus producing steam inreboiler 62 which is charged into the lower portion of column 42 as thestripping agent to remove the last traces of aromatic solute from therich solvent residue in the lower portion of the column.

The rich solvent stream, as it descends through the distillation sectionof stripper 42, is progressively stripped by means of the aforementionedsteam introduced into the reboiling section of the column tosubstantially completely remove the non-aromatic and alkylbcnzenecomponents of the hydrocarbon solute present in the rich solvent, thesehydrocarbons being withdrawn together with the stripping stream andvaporized organic solvent (such as glycol), through line 51, asaforesaid. A higher boiling side-cut fraction comprising the desirednaphthalene products of this invention is withdrawn from column 42,together with stripping steam and vaporized solvent, through line 63,liquefied in condenser 64 to form a liquid condensate which is drainedby means of line 65 and through valve 66 into side-cut receiver 67. Theliquid phase collecting in the receiver separates into a hydrocarbonphase and an aqueous, dilute solvent phase containing a greaterproportion of the glycol solvent component than the overhead in receiver48 because of the substantially higher tcmperature of vapor withdrawalof this side-cut fraction.

The hydrocarbon phase in receiver vessel 67 is made up exclusively ofnaphthalene and its homologs which normally are solids melting atrelatively high temperatures and which have a density greater thanwater. Except for the special provision herein of a parafiinic diluentof the naphthalene phase present in receiver vessel 67, the hydrocarbonsdistilled from the rich solvent and collecting in receiver 67 would forma crystalline mass of solid on the bottom of receiver vessel 67. Such asolid phase hydrocarbon would ordinarily be difficult to handle in thepresence of the less dense aqueous phase also present in the receivervessel. In accordance with the present process a volatile paraffinhydrocarbon diluent of low density is continuously maintained withinreceiver vessel 67 to dissolve and dilute the distilled naphthalenes,maintaining the naphthalenes in solution in the parafiin diluent as'aliquid layer, reducing the density of the by drocarbon phase therebybelow the specific gravity of water and maintaining the hydrocarbonphase as an upper liquid layer in the receiver vessel. For this purposeit is preferred that the amount of light paraflin, such as theaforementioned octane fraction, maintained within the receiver vessel besufiicient to provide at least 0.1 volume of light paraflin per volumeof naphthalene distillate and preferably from about 1 to l to about 10to 1 volumes per volume. The paraflin diluent is supplied to receivervessel 67 through line 68 by recycle of the same paraflin diluentdistilled from a previously recovered upper layer in a subsequentdistillation, as hereinafter more fully described. The lower aqueousphase distilled from the rich solvent in column 42 separating as a loweraqueous layer in receiver 67 collects in the dense liquid leg 69 of thereceiver vessel and is desirably decanted therefrom by continuouswithdrawal through line 70 which connects with line 57 for recycle tothe reboiling section of column 42 through line 59, into reboiler 62 tothereby form the stripping steam supplied to column 42. The loweraqueous phase also contains all of the organic solvent (such as glycol)distilled from the rich solvent as the side out fraction; by recyclingthe lower aqueous phase into column 42, the water thus returned not onlyprovides steam per stripping solute from the rich solvent, but theorganic solvent contained therein is returned to the process flow forrecycle in the system.

The diluted naphthalene layer accumulating above the aqueous phase inreceiver 67 and containing the light from through line and valve 76 intoreboiler 74 from which the resulting heated bottoms and light paraflindiluent are returned to the column through line 77 and valve 78 forfurther vaporization of paraffin diluent therefrom. The vapors of lightparafiin are taken overhead from column 73 through line 79, liquefied incondenser 80 and the resulting condensate drained into receiver 81 fromwhich it is transferred through line 82 by means of pump 83 into line 68and valve 84 for recycle into extract receiver vessel 67. It will thusbe noted that the light parafiin diluent which serves to maintain thenaphthalene extract collected in receiver vessel 67 in liquid phase iscontinuously supplied thereto in a closed circuit, being recycled to theextract receiver 67 from the overhead of extract fractionator 73 andreturned again to continu ously repeat the cycle to extract fractionator73 from which it is again vaporized and recycled to extract re ceiver67.

The bottoms from column 73 comprising the naph thalene extract fromwhich the light parafl'ln diluent has been distilled and comprising amixture of naphthalene and its homologues initially present in the feedstock is withdrawn from reboiler 74 through line 85 by means of pump 86,transferred via line 87 through valve 88 into naphthalene separationcolumn 89 for fractionation of "themixed naphthalene and homologues intoseparate components. The heat supplied for distillation andfractionation of the naphthalene mixture is supplied through reboilfer90, the bottoms from column 89 being withdrawn through line 91, valve92, heated in said reboiler 90 and the resulting vapors and heatedliquid being returned to the column through line 93 and valve 94. Themost volatile vapors fractionated in column 89 are removed as anoverhead vapor from the column through line 95, condensed to a liquidcondensate in cooler 96 and the condensate collected in receiver vessel97. This condensate which consists exclusively of naphthalene as thenaphthalene extract component of greatest volatility is essentially purenaphthalene, free of its higher homologues by virtue of thefractionation in column 89 and control of the overhead vaportemperature. This product may be withdrawn from receiver 97 through line98 and valve 99 into storage or for other disposition as a substantiallypure naphthalene product. Preferably, however, at least a portion of thenaphthalene condensate is returned as reflux to naphthalene distillationcolumn 89 by withdrawing from line 98 at least a portion of thecondensate through line 100, by means of pump 101 which discharges thenaphthalene condensate into reflux return line 102. This reflux isdesirably returned in limited amounts, controlled by valve 103, to theupper plate of fractionating column 89 to provide thereby the desireddegree of fractionation in the column.

The bottoms from the naphthalene column are transferred by means of pump104 from reboiler 94 through line 105 and valve 106 into line 107 whichconveys the bottoms of column 89 into methylnaphthalene separationcolumn 108. The methylnaphthalene in the bottoms is a mixture of itsalpha and beta isomers, which are distilled overhead from column 108through line 109 into cooler 110 which operates at a temperaturesufliciently below the boiling point, but above the melting point of thedistillate to liquefy the methylnaphthalene. The resulting liquidcondensate is withdrawn from cooler 110 into receiver 111 from whichmethylnaphthalene may be withdrawn as a product through line 112 andvalve 113. At least a portion of the methylnaphthalene condensate inreceiver vessel 111 is preferably refluxed to the uppermost. plate incolumn 108 by withdrawing a portion of the condensate from line 112 andtransferring the same by'means of pump 114 through line 115 and valve116 to said upper plate. tionati'on is introduced into the liquidbottoms of column 108, withdrawn therefrom through line 117, by meansofreboiler 118, the. heated bottoms being recycled back to column 108through line 119. The net bottoms make, comprising higher boilinghomologues of naphthalene, such as dimethylnaphthalene, etc. are removedfrom the process flow through line 120 and valve 121 for furtherprocessing, as desired.

.The solvent residue from which substantially all of the volatilehydrocarbon components have been removed by vaporization and strippingin extract stripper 42 is withdrawn from column 42 as a high boilingresidue through line 122 and Valve 123, a major proportion thereof beingrecycled to the lean solvent inlet of extract temperature, or, in theevent that the solvent residue in.

the, lower portion of stripper 42 is at a temperaure below the desiredextraction temperature, heat exchanger 126 may be a heater for raisingthe temperature of the lean solvent to thedesired extractiontemperature. In general,

Heat for the above indicated frac however, vaporization of the solutefrom the rich solvent is effected predominantly by pressure reduction,thereby providing substantially isothermal stripping ofthe rich" solventstream. The lean solvent leaving the bottom of" the stripper for recycletoextraction column 6 is usually at approximately the desired extractiontemperature and may be recycled to column 6 without heating or cooling.Pump also increases the pressure on the lean solvent recycle to theoperating pressure maintained in extractor 6, as previously described,thus restoring the pressure dilferential between extraction zone 6 andthe primary flash zone of extract stripper 42.

In the preferred operation of column 42; at least a portion of thesolvent residue accumulating in the lower.

section of the column is separately reboiled in order to generate steamwhich supplies the stripping agent for recovery of the aromaticsolute'from the rich solvent in column 42. For thispurpose a portion ofthe lean solvent residue from line 122 is withdrawn therefrom throughline 127 in an amount determined by valve 128, mixed with recycle watersupplied through line 59 by connection of line 59 with line 127, andreboiled in heater 62. The steam and hot solvent residue thus producedleave reboiler 62 through line 129 for discharge into the stripping.section of column 42, as heretofore indicated. The steam thus chargedinto the lower section of column 42reconstitutes the solvent to itsdesired selected composition for use as a lean solvent in extractioncolumn 6, steam distills the aromatic extract from the rich solvent, andreducesthe boiling point of the rich solvent. For the purpose ofmaintaining the solvent composition at its desired water content,samples of the lean solvent may be withdrawn from line 122 for analysisand adjustment in water content to the preferred selected compositionfor extraction purposes in column 6.

One of the preferred means of maintaining the glycol solvent componentin its unaltered form, that is, as aglycol of the same identity as thecomponent of the solvent composition initially charged into the processand to avoid the development of acidic and resinous or tarry by-productsin the composition, comprises main taining a blanket of an inert gasover the glycol vaporized from the rich solvent in stripping column 42and returned to the process by recycle of the lower aqueous. phases inthe various receiver vessels attached to overhead and side cut linesfrom column 42. By this means, oxygen which unavoidably leaks into thereceiving ves:- sels and ordinarily absorbed by the glycol solvent isexcluded from the system, thereby eliminating the major cause of glycoldeterioration in an extraction process utilizing glycol solvents. Asuitable means for maintaining such a blanket of inert gas over theaqueous layers in the. receiver vessels comprises introducing the inertgas,

such as nitrogen, carbon monoxide, etc. into one end of each of thereceivers and withdrawing the inert gas from the other end. Thus, inoverhead receiver vessel 48, the

inert gas is admitted into the receiver through line 128 and valve. 129,the gas flowing across the vessel, completely covering the liquidcontents of the receiver and excluding air therefrom, being withdrawnfrom the' vessel through line 130 and valve 131. in order to blanket heaqueous solvent in side cut receiver vessel 67 an inert gas inlet line132 containing valve 133 may be connected to receiver 67 and the gasvented, after passing through the receiver, through line 134 and valve135.

This invention is further illustrated with respect to several of itsembodiments in the following example, the

15 Platforming process to separate a gasoline boiling range cut from thePlatformate having an end boiling point of 400 F. The bottoms whichrepresents that portion of the Platformate product boiling above about400 F. constitutes approximately 3.5% of the total Platformate productand consists almost exclusively of aromatic hydrocarbons, including 20%by weight of naphthalene and 26% by Weight of methylnaphthalene, theremaining aromatic components comprising benzene hydrocarbons of 11, 12and 13 carbon atoms per molecule, the carbon atoms being present in oneor more alltyl side chains attached to the benzene nucleus. The originalPlatformate from which the bottoms cut boiling above 400 F. wasseparated as still residue Was prepared in a prior Platforming processby passing a mixture of a straight-run gasoline fraction having an endboiling point of 400 F. and hydrogen (utilizing a hydrogen tohydrocarbon mole ratio of 9:1) at 950 F. and at a pressure of 500 poundsper square inch over a Platforming catalyst comprising a platinumsupported on an alumina-halogen composite. The residue of the Platformedproduct Was separated by fractionally distilling the Platformingeffluent, taking overhead the aforementioned gasoline boiling rangefraction having an end boiling point of 400 F. from the bottoms residueand the latter utilized as feed stock.

The above bottoms fraction, consisting almost entirely of aromaticcomponents, is a relatively difficult feed stock from which to separateits naphthalene and methylnaphthalene components, because of its highlyaromatic character, dissolving substantially in its entirety in theusual solvent compositions selective for aromatic hydrocarbons withoutproducing a separable raflinate in which the undesired components of thefraction are concentrated. In accordance with the present process,separati n of an aromatic concentrate by solvent extraction is effectedby charging a low molecular weight paraflinic reflux stream into theextraction zone with the selective solvent and the feed stock, the lightparaffins diluting the aromatic-rich feed, reducing its viscosity, itsdensity, and its total miscibility with the solvent and enables theproduction or a naphthalene product of substantially 100% purity.

The above feed stock is charged at a temperature of 375 F., at a rate of1000 barrels per day and at a pressure of 100 pounds per square inch onthe thirtieth tray of a countercurrent solvent extraction columncontaining sixty decks. A solvent composition consisting of 98.2% byweight of diethylene glycol and 1.8% by weight of Water at a temperatureof 380 F. and at the aforementioned pressure, is charged into the top ofthe solvent extraction zone at a rate of 6500 barrels per day. A refluxhydrocarbon stream derived in part from an overhead stream of thestripping column utilized to separate the hydrocarbon solute from therich solvent stream formed in the extraction zone and in part from thelight parafiin fraction recovered from the raflinate stream of theextraction zone is charged at a rate of 1700 barrels per day into thebottom of the extraction column. Analysis of this reflux streamindicates that it is made up of approximately 850 barrels per day ofoctanes, approximately 690 barrels per day of naphthalenes, and theremainder comprises monocyclic aromatic hydrocarbons stripped from therich solvent stream in the subsequent stripping zone. A raffinate streamcomprising the nonextracted components of the combined feed and refluxstreams is removed from the top of the extraction column at a rate of1100 barrels per day, the raffinate retaining only a very smallproportion of the naphthalene hydrocarbons present in the original feedstock and substantially all of the monocyclic aromatics contained in thefeed. The raflinate was diverted, after being washed with a stream ofwater to thereby recover the glycol therefrom, into a ralli'natefractionator wherein the octane components is distilled therefrom andthe latter re- 16 cycled to the reflux line leading into the bottom ofthe extraction zone.

The rich solvent stream formed in the extraction column, at atemperature of 347 F. and at the extractor pressure, that is at poundsper equare inch, is re- ,moved from the bottom of the extraction zone,heated to a temperature of 370 F. and charged into the top of a flashstripping column wherein the pressure is reduced in three stages toatmospheric pressure. In the first stage the pressure is reduced toapproximately 50 pounds per square inch, resulting in the flashdistillation of a light vapor overhead from the top plate of thestripping column which is separated from the lower plates by aside-to-side pan sealed circumferentially on the inside of the strippingcolumn. The overhead vapor at 370 F. is flashed off at a rate ofapproximately 675 barrels per day being thereafter blended with theoctane overhead from the raffinate fractionator and the combined streamrecycled as reflux to the bottom of the extractor. The overhead vaporalso contains a portion of the desired naphthalene and methylnaphthaleneas well as most of the monocyclic aromatics extracted from the originalfeed stock by the solvent. In order to prevent a build-up of monocyclicaromatics in the reflux stream, a portion of the overhead from thestripping column, amounting to the net monocyclic aromatic componentcharged into the system as fresh feed and not removed from the processin the raflinate (about 8 barrels per day) is withdrawn from thestripper overhead stream. A portion of the overhead vapors in the amountof approximately barrels per day comprises the diethylene glycol andwater components of the solvent, these being separated from the overheadvapors in a receiver vessel attached to the overhead vapor condenser,the aqueous solvent being separated by decantation from the upper layerreflux hydrocarbons, combined with other aqueous glycol condensates, andcharged into the reboiling section of the stripping column.

The rich solvent residue is continuously drained from the primary stageflashing section into a secondary flash section wherein the pressure isreduced from 50 pounds per square inch to 5 pounds per square inch, theresulting secondary flash vapors being taken off at 370 F. at a rate ofapproximately 1450 liquid barrels per day, of which 750 barrels per dayrepresents hydrocarbons comprising predominantly aromatic components,together with the remaining octanes present in the rich solvent andapproximately 700 barrels per day of aqueous glycol. The vapors arecondensed by cooling to form a two-layer liquid condensate in thereceiver vessel attached to the secondary flash condenser, the glycollayer being drained from the receiver, mixed with the overhead aqueousglycol and charged into the stripper reboiler to provide stripping steamfor the column. The hydrocarbon portion of the secondary flash overheadis combined with the hydrocarbon portion of the primary flash overheadand recycled as reflux to the extraction column. The rich solventresidue thereafter flows into the stripping section of the columnwherein the pressure on the rich solvent is reduced to atmospheric. Aresulting sidecut fraction is recovered from the stripping zone at atemperature of 374 F., the vapors comprising a mixture. of aqueousglycol and the hydrocarbon portion comprising predominantly naphthaleneand methylnaphthalenc extract. These vapors are cooled sufliciently toform a liquid condensate which is drained into a receiver vessel. Theaqueous glycol liquid layer is drained from the" bottom of the receiver,mixed with the aforementioned aqueous glycol layers, and charged intothe reboiling section of the stripping column to provide strippingsteam. A light liquid paraffin stream comprising the octane fraction(overhead) recovered from the subsequent extract fractionator andcontinuously recycled from the extract -fract'ionator in the amount of222 barrels per day is charged into the extract receiver in order tomaintain vessel.

the naphthalene ,e omponents of. the side-cut fraction in liquid phaseand to reduce the density of the naphthalene sufliciently to maintainthe hydrocarbon distillate of the extract in liquid phase as an upperlayer in the receiver The octanes completely dissolve the normally'solid naphth'alenes in the upperhy'clrocarbon'layer of the receivercontents, the resulting liquid layer being. re-

moved to an extract fractionating column for recovery of the individualcomponents, as hereinafter described.

A reboiler coil is operated as an adjunct to the stripping column,consisting essentially of a gas-fired heater into which the strippedsolvent bottoms is charged and heated to a temperature of 380 F. andinto which the aqueous solvent phases of the various receiving vesselsheretofore referred to are charged in order to generate steam suppliedto the lower portion of the stripping column for vaporization of thearomatic solute from the rich solvent residue. A lean solvent streamcontaining approximatley 1.8% water is continuously removed from thereboiler at a rate of 6500 barrels per day and pumped into-the top ofthe extraction vessel for use as selective solvent therein.

The bottoms of the extract fractionator from which the octane reflux hasbeen removed for recycle to the extract receiver is removed from theextract fractionator at a temperature of 450 F. and at a rate of 405barrels per day into a naphthalene fractionating column from which 184barrels per day of naphthalene of 99.9% purity is taken overhead at atemperature of 424 F. The product crystallizes readily, the crystalsmelting at 802 C. The bottoms fraction from the naphthalene column, at atemperature of 480 F. is charged into a methylnaphthalene separationcolumn from which an overhead fraction (B. P. 468 F.) in the amount of215 barrels per day is recovered. This fraction contains both thealphaand beta-methylnaphthalene isomers and contains approximately 1% byweight of monocyclic aro matics. A bottoms fraction is recovered fromthe methylnaphthalene tower at a temperature of 510 F. in an amountrepresenting approximately 4 barrels per day. This residue containsmonocyclic aromatic hydrocarbons having about 13 carbon atoms permolecule, as well as a small proportion of alkyl naphthalenes of highermolecular weight than methylnaphthalenes.

In the above process nitrogen was charged into the overhead receiversand side cut receiver in order to blanket the surface of the aqueousglycol phase with an inert gas and thereby prevent absorption of oxygenby the glycol. For this purpose, nitrogen was bled into the receivers ata rate of 100 ft. per hour, being removed from the opposite ends of eachof the receiver vessels. In this manner the glycol was maintained in anunaltered condition for long periods of use, the glycol replacement ratebeing less than 1.5 barrels per day on the above plant.

Prior to use of the above nitrogen blanket on the aqueous glycol phase,however, the receiver vessels permitted sufiicient leakage of air intothe unit to rapidly deteriorate the glycol. It was observed that asoperation of the unit continued beyond the first day on stream, the pHof the glycol decreased rapidly, causing rapid corrosion of the steelequipment, formation of tar and loss of glycol from the unit at a rateof more than 60 barrels per day. Glycol deterioration became so rapidthat an auxiliary glycol still was required to continuously distill aslip stream of the solvent for removal of tars and degradation products.

I claim as my invention:

1. A process for recovering a naphthalene hydrocarbon from a mixturecontaining naphthalene and benzene hydrocarbons which comprisessubjecting said mixture to countercurrent contact with an aqueoussolution of solvent in which said naphthalene hydrocarbon is selectivelysoluble and selected from the group consisting of an aliphatic alcoholcontaining up to carbon atoms, an alkylene glycol, a polyalkyleneglycol, anda -glycol-ether,-.at a temperature of from about 200 F. toabout 450 and at a pressure suflicient. to maintain the mixture insubstantially liquidphase, thereby formingsa rich solvent containingsaid naphthalenehydrocarbon dissolved in'said solvent, countercurrentlycontacting the resulting .rich solvent with a liquid paraffinic refluxhydrocarbon which boils at a temperature below the boiling point of thelowest boiling naphthalene hydrocarbon in said mixture, sep arating saidrich solvent from a raffinate comprising the non-extracted portion ofsaid mixture and at least a portion of said paraflinic refluxhydrocarbon, stripping hydrocarbon extract from said rich solvent,separately recovering hydrocarbon extract from the resulting leansolvent, recycling said lean solvent to the first-mentioned contactingstep and separating a naphthalene hydrocarbon from said extract.

2. The process of claim 1 further characterized in that said solvent isan alkylene glycol.

3. The process of claim 2 further characterized in that said alkyleneglycol is an ethylene glycol.

4. The process of claim 1 further characterized in that said solvent isdiethylene glycol containing from 0.5 to about 10% by weight of water.

5. The process of claim 1 further characterized in that said solvent istriethylene glycol containing from 0.5 to about 10% by weight of water.

6. The process of claim 1 further characterized in that said mixtureboils from about 300 to about 500 F.

7. The process of claim 1 further characterized in that said paratfinicreflux hydrocarbon is an octane and said naphthalene hydrocarbon isnaphthalene and the alphaand beta-isomers of methylnaphthalene.

8. The process of claim 1 further characterized in that saidfirst-mentioned contacting step is effected at a temperature of fromabout 300 to about 400 F.

9. The process of claim 8 further characterized in that said extractstripping step is effected by reducing the pressure on said richsolvent.

10. The process of claim 1 further characterized in that the lowestboiling overhead fraction from said extract stripping step is recoveredseparately from a naphthalenerich fraction stripped from said richsolvent and said vapor overhead fraction, in admixture with saidparaffinic reflux hydrocarbon is recycled to said contacting step.

11. The process of claim 10 further characterized in that saidnaphthalene-rich fraction separately collected in said stripping step iscontinuously mixed with a light, normally liquid paraflinic diluent inan amount of said diluent suflicient to completely dissolve thenaphthalenerich fraction and maintain said fraction in liquid phase.

12. The process of claim 11 further characterized in that thediluent-naphthalene-rich mixture is continuously distilled and theseparated light parafiin hydrocarbon continuously recycled to form saiddiluent-aromatic rich mixture.

13. A process for recovering naphthalene and methylnaphthalene from ahydrocarbon fraction boiling from about 400 to about 500 F. andcontaining alkylbenzenesv of 11 to 13 carbon atoms which comprisescontacting said fraction at a temperature of from about 300 to about 400F. and at superatmospheric pressure with a solvent selectively misciblewith aromatic hydrocarbons comprising diethylene glycol containing from0.5 to about 10% by weight of water to form thereby a rich solvent and arafiinate, countercurrently contacting said rich solvent with a lightparaffin reflux hydrocarbon to thereby displace from said rich solventsaid alkylbenzenes, distilling said rallinate and recovering a recyclefraction of said light paraffin reflux, reducing the pressure on saidrich solvent to thereby flash overhead from the rich solvent residue alight hydrocarbon fraction, combining said light hydrocarbon fractionwith said light paraffin reflux re- 19 20 v. e'y'cle'," distilling the"rich solvent residue to recover a naph- References (media the file ofthis patent th alene-niethylnaphthalene extract substantially free of 1non naphthalene contaminants, and distilling said extract UNITED STATESPATENTS into a naphthalene product and a separately recovered 2,037,677Connolly et a1. Apr. 14, 1936 methylnaphthalene product. 5 2,400,802Arnold .L .May 21; 1946 14. The process of claim 13 furthercharacterized in 2,727,854 Brown et al Dec.v 20, 1955 i that said lightparaffin reflux is the octane to decane frac- 2,770,663 Grote Nov. 13,1956 v tion of a gasoline boiling range material.

1. A PROCESS FOR RECOVERING A NAPHTHALENE HYDROCARBON FROM A MIXTURECONTAINING NAPHTHALENE AND BENZENE HYDROCARBONS WHICH COMPRISESSUBJECTING SAID MIXTURE TO COUNTERCURRENT CONTACT WITH AN AQUEOUSSOLUTION OF SOLVENT IN WHICH SAID NAPHTHALENE HYDROCARBON IS SELECTIVELYSOLUBLE AND SELECTED FROM THE GROUP CONSISTING OF AN ALIPHATIC ALCOHOLCONTAINING UP TO 10 CARBON ATOMS, AN ALKYLENE GLYCOL, A POLYALKYLENEGLYCOL, AND A GLYCOL ETHER, AT A TEMPERATURE OF FROM ABOUT 200*F. TOABOUT 450*F. AND AT A PRESSURE SUFFICIENT TO MAINTAIN THE MIXTURE INSUBSTANTIALLY LIQUID PHASE, THEREBY FORMING A RICH SOLVENT CONTAININGSAID NAPHTHALENE HYDROCARBON DISSOLVED IN SAID SOLVENT, COUNTERCURRENTLYCONTACTING THE RESULTING RICH SOLVENT WITH A LIQUID PARAFFINIC REFLUXHYDROCARBON WHICH BOILS AT A TEMPERATURE BELOW THE BOILING POINT OF THELOWEST BOILING NAPHTHALENE HYDROCARBON IN SAID MIXTURE, SEPARATING SAIDRICH SOLVENT FROM A RAFFINATE COMPRISING THE NON-EXTRACTED PORTION OFSAID MIXTURE AND AT LEAST A PORTION OF SAID PARAFFINIC REFLUXHYDROCARBON, STRIPPING HYDROCARBON EXTRACT FROM SAID RICH SOLVENT,SEPARATELY RECOVERING HYDROCARBON EXTRACT FROM THE RESULTING LEANSOLVENT, RECYCLING SAID LEAN SOLVENT TO THE FIRST-MENTIONED CONTACTINGSTEP AND SEPARATING A NAPHTHALENE HYDROCARBON FROM SAID EXTRACT.